1. Field of the Invention
The present invention relates to an installation structure for a gas sensor, which can perform accurate detection.
2. Description of the Related Art
As an installation structure for a gas sensor, there is for example that shown in Japanese Unexamined Patent Application, First Publication No. Hei 9-5278. Explaining this by means of FIG. 7, reference symbol 41 denotes a sensor base. On the surface side of the sensor base 41 is formed a gas detection mechanism 44 which is provided with a reference element 42 and a detection element 43, and these are covered by a cover 45. The top of the cover 45 is of reduced diameter, with a cylindrical cavity end opening blocked by a flow velocity reducing member 46. An empty space within a reduced diameter cylinder wall 47 is formed as a deceleration inlet 48. Moreover, the base end side within the cover 45 is configured as a diffusion chamber 49.
A gas sensor S constructed in this way is attached along the sensor base 41 to an outer wall of a target detection gas passage 50 so as to protrude inside the passage 50.
Also, for example, an installation structure for a gas sensor shown in Japanese Unexamined Patent Application, First Publication No. Hei 9-170994 is known. As shown in FIG. 8, a sensor installation box 54 is attached in a position corresponding to a gas inlet port 53 in an outer wall 52 of a target detection gas passage 50, and by matching a communicating hole 55 of the sensor installation box 54 with the gas inlet port 53, the sensor installation box 54 is communicated with the interior of the passage 50, and a gas sensor S′ is attached to a bottom wall 56 of the sensor installation box 54.
The former installation structure is superior in the point that influence from the flow velocity of the target detection gas is suppressed as much as possible, so that conditions in which there is no flow velocity in the diffusion chamber 49 can be created. However, in relation to the cover 45 protruding into the passage 50, there is a problem in that this causes disturbance of the target detection gas flowing through the passage 50, so that concentration fluctuations arise in the target detection gas taken in to inside the cover 45, before arriving at the diffusion chamber 49, and hence accurate detection is not possible.
On the other hand, the latter installation structure has the advantage of being able to detect with minimal influence from the flow velocity, by retaining the target detection gas inside the sensor installation box 54 under conditions where there is no flow velocity. However, there is the problem in that when stagnation arises inside the sensor installation box 54 due to the target detection gas not being replaced enough inside the comparatively wide sensor installation box 54, is not possible to obtain an accurate gas concentration measure of the target detection gas passing through the passage 50 at that time.